High efficiency, high power density, high reliability and a low cost have always been requirements for a power converter in the field of electrical and electronic devices. High efficiency means energy consumption reduction, energy conservation, emission reduction, environment protection, and a reduced operating cost. High power density means a compact dimension and a light weight, a reduced transportation cost and occupied space as well as saving material resource, so as to reduce a manufacturing cost. High reliability means a longer service life and a lower maintenance cost.
For a power converter, a semiconductor device is one of the major decisive factors to the efficiency. With the development of power converters, modularization of semiconductor devices has become a significant developing trend. Power module packages are also becoming lighter, thinner, shorter and smaller. With the sizes of the power semiconductor device packages becoming smaller, requirement for heat dissipation is growing higher.
FIG. 1 is a cross-sectional view of a conventional quad flat none-lead package (QFN) structure. As shown in FIG. 1, a die 1 is usually surface-mounted on a lead frame 2 via epoxy 5, and then a pad on an upper surface of the die 1 is coupled to a pin of the lead frame 2 through wire bonding, and finally, the die 1, a bonding wire 3 and the lead frame 2 are packaged into an integral body through molding compound 4. Although the packaged structure has advantages of a simple structure, a small package size and high operation efficiency of a system board, etc., there are also obvious problems in heat dissipation. In this structure, the die is surface-mounted on the lead frame, and the lead frame is surface-mounted as an electrode on the system board (not shown in the drawing), therefore, heat generated by the die during operation is dissipated onto the system board through the lead frame right below the die. Most of heat generated by the die will be transferred onto the system board, it will impede effective function of other components on system board (such as a drive unit, a control unit, and the like) Therefore, in practical application, sufficient space is required to be reserved on the system board to prevent the influence to the drive unit and control unit caused by heat, and a specialized heat-dissipation design is required, so as to achieve the purpose of effective heat dissipation.
FIGS. 2A to 2C are cross-sectional views of a dual inline package (DIP) structure. Since a pin of a lead frame 24 is disposed outside of molding compound 25 and occupies certain space, the design of the pins is not beneficial to save system space, and thus needs to be optimized. In addition, since the pin of the lead frame 24 is disposed outside of the molding compound 25, one cavity is required for one module in molding, that is, one mold is required for one kind of size of a package. Thereby, a new mold has to be replaced when the size of the module is changed, thus increasing production costs of power modules due to production of different-sizes of molds. In practical application, in order to avoid the investment in molds, universality of a mold has to be taken into consideration in designing, resulting in limits on the design.